Add scroll_offset and scroll_snap to transform_node's traced value

BUG=644514
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2340663002
Cr-Commit-Position: refs/heads/master@{#418589}

cc/trees/transform_node.cc

@@ -231,6 +231,8 @@ void TransformNode::AsValueInto(base::trace_event::TracedValue* value) const {
   value->SetInteger("content_target_id", 0);
   value->SetInteger("source_node_id", source_node_id);
   value->SetInteger("sorting_context_id", sorting_context_id);
+  MathUtil::AddToTracedValue("scroll_offset", scroll_offset, value);
+  MathUtil::AddToTracedValue("scroll_snap", scroll_snap, value);
 }
 
 TransformCachedNodeData::TransformCachedNodeData()